A conventional apparatus for controlling an electrically-driven vehicle generally has a structure that a plurality of induction motors, each attached to each of a plurality of axles on a truck, is driven together in parallel by a single inverter (for example, see Patent Document 1 below).
A technical problem in driving the induction motors together in parallel by a single inverter is in accommodating with different degrees of wear in diameters of a plurality of wheels (hereinafter, referred to as “wheel diameter”) that are driven together by a single inverter.
It is well known that the rotation speed of an induction motor (=rotor frequency) is a value obtained by adding a slip frequency to an inverter frequency. The slip frequency has a significant meaning when induction motors are driven by a single inverter, because the slip frequency absorbs the difference between the inverter frequencies that are common among the induction motors and the rotor frequencies that are different among the induction motors.
More specific explanation will now be provided, using an example where a plurality of wheels are rotating on rails without slipping thereon.
The rotation speed of a motor becomes lower than those of others when a wheel diameter is greater (that is, a circumferential length thereof is longer) than the others. On the contrary, when the wheel diameter is smaller (that is, a circumferential length thereof is shorter), the rotation speed of the motor becomes higher. Because the inverter frequency is common among the motors, a difference in rotation speed is a difference in slip frequency applied to each of the induction motors. At this time, different degrees of torques are generated in the induction motors, correspondingly to the difference in the slip frequencies. However, because a rated slip frequency of an induction motor is generally set in such a manner that an expectable difference in the wheel diameter does not give any influence thereto, the generated torque difference is very limited and practically does not result in a problem.
Therefore, along with other advantages, it is suitable to use induction motors for driving motors together in parallel by a single inverter. In addition, by using the structure to drive induction motors by a single inverter, the number of inverters can be minimized, regardless of the number of induction motors installed on a vehicle. In this manner, the controlling apparatus can further be reduced both in weight and size.
Recently, a permanent magnet synchronous motor driven by an inverter is increasingly applied in fields such as industrial equipment or home appliances.
In comparison to an induction motor, a permanent magnet synchronous motor has advantages of not requiring an excitation current, because magnetic fluxes are established by permanent magnets, and of being highly efficient, because no current flows into the rotor, thus not causing a secondary copper loss. For these reasons, recently, various attempts have been made to apply a permanent magnet synchronous motor as a motor for driving an electric vehicle.
[Patent Document 1] Japanese Patent Application Laid-open No. 2006-014489
Disclosure of Invention
Problem to be Solved by the Invention
When applying a permanent magnet synchronous motor as a motor for driving an electric vehicle, minimizing of a structure of an apparatus including a plurality of permanent magnet synchronous motors is a critical matter.
Furthermore, as well known in the art, a permanent magnet synchronous motor operates with the inverter frequency synchronized with the rotor frequency. Therefore, permanent magnet synchronous motors, each differing in the rotation speed, cannot be driven together in parallel by a single inverter.
Therefore, if a permanent magnet synchronous motor is applied to an electric vehicle, a driving inverter will be required for each of the permanent magnet synchronous motors. Because, in an electric vehicle, each wheel is driven by a plurality of motors in a vehicle set, the number of required inverters increases. Therefore, a controller for the increased inverters becomes larger in size and cost. Thus, the controlling apparatus inevitably increases in size, mass, and cost.
The present invention is made in consideration of the above. An object of the present invention is to provide a motor controlling apparatus, having a controller for a plurality of inverters provided corresponding to each of a plurality of motors, where each of calculation units, to be arranged accordingly to each of the motors, is arranged effectively within a controller, and operations performed thereby are effectively grouped so as to reduce the size, the mass, and the cost thereof.
Means for Solving Problem
In order to solve the afore-mentioned problem and attain the object, a motor controlling apparatus for controlling a plurality of alternating-current motors is constructed in such a manner that it comprises: a direct-current voltage source; a plurality of inverters that are provided correspondingly to each of the alternating-current motors, and outputs an alternating-current voltage at a predetermined frequency obtained by converting a direct-current voltage supplied from the direct-current voltage source to each of the alternating-current motors; a contactor that opens and closes an output end of each of the inverters; a voltage detector that detects the direct-current voltage supplied to each of the inverters; a current detector that detects a current in each of the alternating-current motors; and a controller that outputs at least a control signal to the inverters based on a control command supplied externally, the voltage detected by the voltage detector, the current detected by the current detector, and a signal indicating conditions of rotations of the alternating-current motors, wherein the controller includes: a first common calculation unit having: a sequence processor that generates and outputs a first control signal that relates to generation of a torque command, based on a drive command signal input externally, and a protection detector that detects an abnormality in the alternating-current motors and the motor controlling apparatus, and generates a second control signal indicating the abnormality to cause the inverters to stop; a second common calculation unit having a basic torque command generator that generates and outputs a basic torque command that is common to the inverters based on the first control signal received from the first common calculation unit; an individual calculation unit that individually generates and outputs third control signals individually related to each of the inverters based on the basic torque command received from the second common calculation unit; and a common logic calculation unit that calculates and outputs a first gate signal for controlling switching of each of the inverters based on the second control signals received from the common calculation unit and the third control signals received from a plurality of such individual calculation unit, and is commonly provided to the individual calculation units so as to enable the first gate signals corresponding to each of the inverters to be controlled simultaneously.
Effect of the Invention
In a motor controlling apparatus according to the present invention, calculation units in the controller are grouped into: the common calculation unit that calculates and outputs control signals that are common among inverters; the individual calculation unit that individually calculates and outputs control signals related to each of the inverters; and the common logic calculation unit that outputs gate signals for controlling switching of each of the inverters based on signals received from the common calculation units and the individual calculation units. Thus, operations performed by each of the calculation units are effectively grouped, and each of the calculation units, arranged in accordance with each of the motors, is effectively arranged within a controller. Therefore, the present invention achieves the effects to reduce the size, the mass, and the cost of the motor controlling apparatus.